1. Field of the Invention
The present invention relates to an optical recording card and a method of producing the same. More particularly, it relates to preformatting pits in the optical recording medium of the optical recording card.
In recent years a number of cards in which various kinds of informations are recorded are increasingly put in practical use.
2. Description of the Prior Art
This kind of card is required to record various kinds of informations such as data concerning individual person, data concerning a company from which the card is issued or the like data. In the earier age such informations were recorded using visual characters and symbols and in the later age they were recorded in response to electrical signals which were generated magnetically. However, the conventional card is required to take adequate measures for preventing data from being falsified and moreover for the current tendency of increased volume of informations.
In view of the current situation as mentioned above an optical recording card to which laser technology is applied to record information has been developed in recent years. The optical card includes an information recording medium (optical recording medium) with an optical reflective surface incorporated therein and it is used in such a manner that data pits are detected with the aid of a laser in dependency on the difference in optical reflection among the data pits to read information therefrom.
The optical recording medium is required to include a plurality of preformatting pits each of which represents an address by means of which the position and the state of usage of track guide grooves and each sector on each of tracks for carrying out tracking during the steps of writing, reading and erasing are shown and the preformatting pits are previously written in the optical recording medium in such a manner that they can not be erased in any way.
A so-called stamping method is hitherto employed for the purpose of forming the preformatting pits as mentioned above.
To facilitate understanding of the present invention it will be helpful that the conventional stamping method as disclosed in U.S. Pat. Nos. 4,301,099 and 4,395,211 will be described below with reference to FIG. 9.
When a plurality of ruggednesses serving as preformatting pit are formed on the optical recording medium, an assembly comprising a transparent base plate 21 made of glass or the like material and a layer of resist 22 deposited on the base plate 21 is subjected to exposing to laser light and thereby a pattern corresponding to arrangement of a plurality of preformatting pits 23 is formed. Thereafter, a master is obtained by plating a nickle film 24 on the thus formed pattern and a die 25 is produced with the aid of a mother stamper which is prepared by utilizing the thus obtained master. Next, by operating the die 25, the preformatting pits 23 are reproduced on a transparent plastic material 26 such as polycarbonate resin, acrylate resin or the like material in accordance with an injection molding process or the like and an aluminum reflective film 27 is placed on the recording surface whereby a required recording medium 20 is produced.
As will be readily apparent from the above description, the conventional steps of producing the recording medium are very complicated and it takes long time until the die is produced, causing a large amount of expenditure to be required for production of the recording medium. Accordingly, it may be concluded that the conventional method is not acceptable in the case of production within a short period of time and production order in the type of multi-kind and small production lot.
Particularly, due to the fact that a plurality of ruggednesses constituting preformatting pits are utilized for carrying out optical reflection, it is necessary that they are formed at a very high accuracy. Accordingly, a considerably large amount of labor is required to control a film thickness of the resist layer, resulting in production in small lots and production of the optical recording medium and the optical recording card at an inexpensive cost being achieved only with much difficulties.